91 350 SDL a/c advice - PeachParts Mercedes-Benz Forum

beerme · #1 05-07-2003, 09:51 AM

My wifes 91 350SDL A/C isn't working correctly. When you turn it on it blows hot air. I had the system checked by an A/C shop and it is good on freon. They said the condensor fans are not kicking on that is why the air isn't cooling. Can anyone here tell me what might be the problem? I am guessing it is a switch that has gone bad but I don't know where to look or how to get started on troubleshooting this. I have to do it myself as this is my wifes work car and we cannot afford to be without it for a few days while it is in shop. Thanks for any and all assistance.....Phil

jcyuhn · #2 05-07-2003, 10:09 AM

Is it cold when driving but gets warm when stopped? The condenser fans only come into play when not moving very fast. At 40MPH the speed of the car provides the air flow over the condenser. If it's not cold on the road, you need a new a/c technician.

- JimY

beerme · #3 05-07-2003, 10:24 AM

No the a/c doesn't get cold at all. I had the car in park in my garage and the a/c on full. The fans didn't come on, further it was blowing out both the defrost area and the dash vents with the temp set at max cold. Also I was driving this morning and I had the a/c on doing 70mph on the highway to work and the air was bascially the same temp as the outside like it was on vent and not a/c.

#4 05-07-2003, 11:18 AM

The condensor fans not coming on is effect, not cause. They come on when the high side pressure reaches a certain point. The purpose is not to make the a/c cool better, the purpose is to bring down high side pressure to protect the system.

Therefore the fact that it is not cooling AND the fans are not coming on indicates a problem, probably a low charge.

Check for leaks, repair the leak then recharge.

Good luck,

jcyuhn · #5 05-07-2003, 11:50 AM

Sounds like you may have multiple problems. The only common point of failure that could cause both the a/c to not run and the air to be directed out the incorrect vents is the pushbutton control unit. But you sure don't hear to many complaints of failure about this part on the 126, so I doubt it's your issue.

Most likely you have a problem with one or more of the vacuum pods which move the little doors which direct the airflow of the climate system. You'll need someone who really knows the climate system to evaluate it. Don't know how difficult replacement is on a 126 - it varies from chassis to chassis.

Are you sure the compressor is operating? Did the shop check the high side/low side pressures? We really can't give you any more diagnosis over the 'net without more information. There are a multitude of possibilities for the has freon/won't cool problem scenario.

- JimY